datastructures interfaces

<?php
use Eos\Datastructures\Immutable;
use Eos\Datastructures\Struct;

class Rectangle extends Struct implements Immutable {
  public $x;
  public $y;
  public $height;
  public $width;
}

$rect = new Rectangle(['x' => 5, 'y' => 6, 'height' => 56, 'width' => 19]);

$rect->x = 5; // will throw ImmutableException

Presumably each with() call would return a new struct instance, but with PHP's copy-on-write the memory impact should be minimal. That's how PSR-7 works, and the initial benchmarks said it was cheap enough to do.

And I guess now I see the point of nullables, since without them a struct would only sort of function. Unless we allowed a property to have a default value defined, so even $r = Rectangle{}; would give a valid set of values. Honestly I think I prefer that to nullable, as nulls are nothing but a source of pain and suffering.

That is, you'd have:

struct Rectangle {
  int $x = 0;
  int $y = 0;
  float $width = 0;
  float $height = 0;
}

$r = Rectangle{};
print $r->x; // prints 0.

That way there's still never a null.